1. Field of the Invention
The invention relates to a device for controlling injection of a liquid embolic composition into a patient, and more particularly, to a device for containment and restraint of a liquid embolic composition during and after solidification. The device for controlling injection may be incorporated in a catheter system used for delivery of the embolic composition in a controlled manner.
2. State of the Art
In many clinical situations it is desirable to selectively occlude blood vessels for a variety of purposes, such as, the control or prevention of bleeding, the prevention of blood supply to tumors, treatment of arterial venous malformations (AVMs), and the blocking of blood flow within an aneurysm. Embolization of blood vessels has been performed by employing certain polymer compositions, particulates, and/or selerosing material including silicone balloons, metallic coils, PVA particles, gelatin, and the like, to selectively block blood flow in the blood vessels. However, these embolization procedures have certain drawbacks.
Intracranial aneurysms are abnormal blood filled dilations of a blood vessel wall which may rupture causing significant bleeding and damage to surrounding brain tissue or death. Traditionally, intracranial aneurysms have been surgically clipped to reduce the risk of rupture by placing a metal clip around the neck of the aneurysm to cut off and prevent further blood flow to the aneurysm. However, many aneurysms cannot be treated surgically because of either the location and configuration of the aneurysm or because the condition of the patient does not permit cranial surgery.
When aneurysms cannot be treated surgically or when surgery is considered to be too risky or invasive, aneurysms may be treated endovascularly with coils. The coils are placed in the aneurysm by extending a catheter endovascularly to the site of the aneurysm and passing single or often multiple metallic coils such as platinum, stainless steel, or tungsten coils through the catheter into the aneurysm. The coils placed within the aneurysm create a thrombus which occludes the aneurysm and prevents further blood flow to the aneurysm. The treatment of intracranial aneurysms with coils isolates the aneurysm from arterial circulation, helping to guard against rupture and further growth of the aneurysm. However, the use of metallic coils to treat intracranial aneurysms may not be a permanent solution because the blood clot around the coils may lyse or dissolve due to the dynamic nature of the blood clotting function. Once a clot formed around the coils in an aneurysm lyses, the coil can no longer perform its function of occluding the aneurysm. In addition, the coils may become dislodged, move from the aneurysm, and enter the patient's blood stream causing blockages at other locations within the vascular system. Coils can also form a loop extending into the blood stream which generates undesirable embolisms downstream.
Another drawback associated with the use of coils to occlude an aneurysm is that the coils are known to compact over time leaving cavities for subsequent aneurysm growth. In addition, if a subsequent surgical clipping procedure is warranted, it can be difficult to place the clip over the coil mass.
Other procedures for treating aneurysms include occluding the aneurysm with a silicone balloon or filling the aneurysm with particulate material.
Aneurysms having large necks are not easily treated by either surgical clipping or by coils because the aneurysm neck may have a shape which cannot be completely clipped surgically and the coils may tend to become dislodged from the aneurysm when the neck is particularly large.
One minimally invasive procedure for treating intracranial aneurysms which addresses the problems with the surgical clipping and coil techniques involves the endovascular injection of a liquid embolic composition which solidifies in the aneurysm to occlude the aneurysm. Typically, liquid embolic compositions include a water insoluble, biocompatible, non -biodegradable polymer, dissolved in a biocompatible solvent. Once the liquid embolic composition is injected into the aneurysm, the biocompatible solvent dissipates into the blood and the polymer solidifies to occlude the blood flow through the aneurysm. These liquid embolic compositions preferably include a radiopaque material which allows the physician to view the embolization procedure by fluoroscopy.
Prior to delivery of the liquid embolic composition to the aneurysm, the aneurysm and delivery device are preferably positioned so that the liquid embolic composition will be delivered by gravity into the aneurysm and will solidify and remain in the aneurysm. This means that the patient position is often manipulated. to position the aneurysm with the aneurysm neck pointing up. As the embolic composition is delivered to the aneurysm, the solvent dissipates from the polymer material and is removed in the blood stream causing the polymer material within the aneurysm to solidify.
Depending on the rate at which the liquid embolic material is injected into the blood vessel and the amount of blood flow present, the polymer may remain in liquid form for a period of time while the solvent dissipates into the blood stream. In addition, the solvent concentration at the point of injection may increase to a point where small strings of unsolidified polymer material may separate from the polymer mass and be carried away in the blood stream where the polymer can occlude an undesired vascular location.
Accordingly, it would be desirable to provide a device or method for controlling the solidification of the polymer material during injection so that an aneurysm which is in a non-gravity dependent position can be filled without causing the liquid embolic composition to pass out of the aneurysm into the blood stream. It would also be desirable to prevent polymer strings from being carried away in the blood stream.